Characterization of electrolytic ZrO2 coating on AISI 316L stainless steel

An electrolytic Zr(OH)(4) gel coating on AISI 316L stainless steel sheets has been investigated. The coating was produced by reduction of a ZrO(NO3)(2) aqueous solution. Thermogravimetric and differential thermal analysis (TGA and DTA, respectively) of the as-formed electrolytic gel Zr(OH)(4) coating were conducted between 298 and 1373 K. Three transitions were observed: the first, being the evaporation of H2O from the surface between 298 and 453 K, followed by the removal of H2O from the gel bulk between 453 and 623 K, and finally, the condensation of Zr(OH)(4) occurred between 623 and 693 K. X-ray diffraction (XRD) revealed crystallization into a tetragonal structure at 723 K, followed by nucleation of a monoclinic structure at 973 K with complete transformation into the monoclinic phase occurring at 1173-1273 K. The electrolytic ZrO2 coating on 316L sheets were annealed at 973 K for 2 h in air or vacuum. The coatings annealed in vacuum show an adhesion strength of over 250 MPa and superior corrosion resistance in 2.5 M HCl and 2.5 M H2SO4 compared with coatings annealed in air. (C) 1999 The Electrochemical Society. S0013-4651 (98)04-067-1. All rights reserved.